Spike (1 weekend): context-aware autocomplete via sqls — vendor vs LSP vs never

Timeboxed evaluation of sqls-server/sqls (completer lives under internal/, so: vendor/fork the code, run it as an LSP subprocess, or decide never). Outcome is a written decision, not code. pgcli-grade completion is a multi-year asset — no commitment without this spike.

**Acceptance:** decision recorded in the issue with effort estimate; follow-up issue created only if go.

Start by reviewing sqls-server/sqls and the completer under internal/. Compare the vendor or fork, LSP subprocess, and no-adoption options, then record the decision and effort estimate in this issue; create a follow-up only if the outcome is to proceed.

Written by the indexing model from the issue text.